1. Field of the Invention
The present invention relates to a slicing method by use of a slicing machine and, in particular, to such slicing method in which a slicing machine is used to slice a cylindrical material into thin pieces.
2. Description of the Related Art
Conventionally, in slicing out a cylindrical material such as a silicon ingot by use of a slicing machine to manufacture semiconductor wafers, after the ingot is lowered by the thickness of the wafer in an axially downward direction from a reference position, the ingot is moved toward a rotating blade (cutting edge) so that the ingot is sliced into the thin semiconductor wafers, each wafer having first and second wafer faces. Alternatively, in a slicing machine which performs the slicing of the wafers and the grinding of the wafer first face simultaneously, after the ingot is lowered downward by the amount of the desired thickness of the wafer plus the width for grinding, while the ingot is being moved toward the cutting edge, the slicing of the wafers and the grinding of the wafer first face are carried out simultaneously. In this case, the grinding width is found empirically from the thickness of the wafer and the like, that is, the grinding width can be determined by the skill or perspection of operators.
However, because the displacement of the blade (cutting edge) while slicing becomes unstable as the number of slicings are increased, the above-mentioned conventional slicing methods are disadvantageous in that they cannot manufacture desired wafers in a stable manner. Also, due to thermal stresses caused by the heats (such as the frictional heat of a bearing, heat generated by a motor and the like) that are generated by ambient temperatures, a coolant and the slicing machine, a relative positional relationship between the blade and the grinding wheel is changed, thereby making it impossible for wafers with high accuracy to be obtained. Further, since the blade and grinding wheel are worn as they repeat the slicing and grinding operations, the amount of grinding and the like are changed accordingly, which causes the wafers to vary in thicknesses. In addition, due to the fact that the amount of grinding of the wafer first face is set with considerable allowance, there is a possibility that the cylindrical material may be ground wastefully, which is not desirable from the viewpoint of costs.